Liquid crystal device and electronic apparatus using the same

ABSTRACT

The liquid crystal device of the present invention effectively prevents reversion of bright/dark states between a reflective display mode and a transmissive display mode. The liquid crystal device includes a first absorptive polarizer, which receives light from outside;a liquid crystal cell, which receives light emitted from the first absorptive polarizer; a second absorptive polarizer, which receives light emitted from the liquid crystal cell; and a reflective polarizer, which receives light emitted from the second absorptive polarizer. The reflective polarizer has an axis of reflection in a predetermined direction to reflect at least part of light that has been transmitted through the first absorptive polarizer, the liquid crystal cell, and the second absorptive polarizer to be incident on the reflective polarizer. The reflective polarizer partially transmits light including a linearly polarized light component which is included in light entering the reflective polarizer from an opposite side to the second absorptive polarizer and which is to be transmitted through the second absorptive polarizer. The first absorptive polarizer has an axis of transmission in a specific direction to cause light, which has been reflected by the reflective polarizer and transmitted through the second absorptive polarizer, to be transmitted through the first absorptive polarizer.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a transflective liquid crystaldevice (hereinafter also referred to as a transflective liquid crystaldevice) capable of both reflective display, which reflects incidentlight to display an image, and transmissive display, which transmitsincident light to display an image.

[0003] 2. Description of the Related Art

[0004] The transflective liquid crystal device is widely used as adisplay device of portable information equipment. FIG. 11 schematicallyillustrates the structure of a conventional transflective liquid crystaldevice 1000. The transflective liquid crystal device 1000 includes anabsorptive polarizer 1020, a liquid crystal cell 1030, a light diffusingplate 1040, a reflective polarizer 1050, and a light absorbing plate1060. A backlight 1070 is further disposed outside the light absorbingplate 1060. The liquid crystal cell 1030 includes a lower glasssubstrate 1033, an upper glass substrate 1031, and a liquid crystallayer 1035 sealed between these glass substrates 1031 and 1033. Aplurality of transparent signal electrodes 1034 are mounted on the uppersurface of the lower glass substrate 1033. A plurality of transparentscanning electrodes 1032 are mounted to be perpendicular to theplurality of signal electrodes 1034 on the lower surface of the upperglass substrate 1031. The liquid crystal cell 1030 has a passive matrixconfiguration, in which one pixel is defined by one signal electrode1034, one scanning electrode 1032, and the liquid crystal layer 1035between these electrodes 1034 and 1032. Namely the light transmittedthrough the liquid crystal layer 1035 is modulated according to thevoltage applied between one signal electrode 1034 and one scanningelectrode 1032. The liquid crystal layer 1035 may be made of a TN(twisted nematic) liquid crystal composition or STN (super twistednematic) liquid crystal composition. A translucent film having thetransmittance of about 50% is used for the light absorbing plate 1060.

[0005]FIG. 12 shows problems arising in the conventional transflectiveliquid crystal device 1000. The absorptive polarizer 1020 has an axis oftransmission 1020T that is set parallel to the plane of the drawing, andan axis of absorption 1020A that is perpendicular to the plane of thedrawing. The reflective polarizer 1050 has, on the other hand, an axisof transmission 1050T that is parallel to the plane of the drawing, andan axis of reflection 1050R that is perpendicular to the plane of thedrawing. The following describes the operations of the liquid crystaldisplay 1000 on the assumption that the polarizing direction of thelight transmitted through the liquid crystal cell 1030 is rotated by 90degrees while no voltage is applied between the signal electrodes 1034and the scanning electrodes 1032 (that is, when the liquid crystal cell1030 is in an OFF state).

[0006] This liquid crystal device 1000 has two display modes, that is, areflective display mode using incident light 1100 from the outside and atransmissive display mode using light 1120 emitted from the backlight1070. In the reflective display mode, when the non-polarized light 1100enters the absorptive polarizer 1020, a linearly polarized lightcomponent having the polarization direction parallel to the axis ofabsorption 1020A is mostly absorbed by the absorptive polarizer 1020,while only a linearly polarized light component having the polarizationdirection parallel to the axis of transmission 1020T is transmittedthrough the absorptive polarizer 1020 and enters the liquid crystal cell1030. The optical rotatory power of the liquid crystal cell 1030 causesthe light component entering the liquid crystal cell 1030 to beconverted into linearly polarized light having a polarizing directionthat is perpendicular to that of the incident light. The polarizingdirection of the light emitted from the liquid crystal cell 1030 issubstantially identical with the direction of the axis of reflection1050R of the reflective polarizer 1050, so that most of the lightemitted from the liquid crystal cell 1030 is reflected by the reflectivepolarizer 1050 and re-enters the liquid crystal cell 1030 as returnlight. The liquid crystal cell 1030 converts the return light intolinearly polarized light having a polarizing direction that isperpendicular to that of the return light. At this moment, thepolarizing direction of the return light emitted from the liquid crystalcell 1030 is substantially identical with the direction of the axis oftransmission 1020T of the absorptive polarizer 1020, so that most of thereturn light emitted from the liquid crystal cell 1030 is transmittedthrough the absorptive polarizer 1020. In the reflective display mode,the pixels where the liquid crystal cell 1030 is in the OFF statereceive the light reflected and returned as discussed above and arethereby observed as bright pixels. The pixels where the liquid crystalcell 1030 is in an ON state are, on the contrary, observed as darkpixels.

[0007] In the transmissive display mode, on the other hand, when thenonpolarized light 1120 enters the reflective polarizer 1050, a linearlypolarized light component having the polarization direction parallel tothe axis of reflection 105OR is mostly reflected by the reflectivepolarizer 1050, while only a linearly polarized light component havingthe polarization direction parallel to the axis of transmission 1050T istransmitted through the reflective polarizer 1050 and enters the liquidcrystal cell 1030. The optical rotatory power of the liquid crystal cell1030 causes polarizing direction of the light transmitted through theliquid crystal cell 1030 to be converted into a direction substantiallyparallel to the axis of absorption 1020A of the absorptive polarizer1020. Most of the light emitted from the liquid crystal cell 1030 isaccordingly absorbed by the absorptive polarizer 1020 and is nottransmitted through the absorptive polarizer 1020. In the transmissivedisplay mode, since the light is absorbed in the course of the opticalpath, the pixels where the liquid crystal cell 1030 is in the OFF stateare observed as dark pixels. The pixels where the liquid crystal cell1030 is in the ON state are, on the contrary observed as bright pixels.The relationship between the ON/OFF state of the liquid crystal cell1030 and the bright/dark state of the pixel in the transmissive displaymode is reverse to that in the reflective display mode. In thetransflective liquid crystal device 1000, the brightness and darkness ofdisplay are reversed between the reflective display mode and thetransmissive display mode.

SUMMARY OF THE INVENTION

[0008] The object of the present invention is thus to provide a liquidcrystal device that effectively prevents the reversion of the samebright/dark states between the reflective display mode and thetransmissive display mode, and also to provide an electronic apparatususing such a liquid crystal device.

[0009] At least part of the above and the other related objects isattained by a liquid crystal device that modulates light responsive togiven image signals. The liquid crystal device includes a firstabsorptive polarizer, which receives light from outside;a liquid crystalcell, which receives light emitted from the first absorptive polarizer;asecond absorptive polarizer, which receives light emitted from theliquid crystal cell; and a reflective polarizer, which receives lightemitted from the second absorptive polarizer. The reflective polarizerhas an axis of reflection in a predetermined direction to reflect atleast part of light that has been transmitted through the firstabsorptive polarizer, the liquid crystal cell, and the second absorptivepolarizer to be incident on the reflective polarizer. The reflectivepolarizer partially transmits light including a linearly polarized lightcomponent which is included in light entering the reflective polarizerfrom an opposite side to the second absorptive polarizer and which is tobe transmitted through the second absorptive polarizer. The firstabsorptive polarizer has an axis of transmission in a specific directionto cause light, which has been reflected by the reflective polarizer andtransmitted through the second absorptive polarizer, to be transmittedthrough the first absorptive polarizer.

[0010] The liquid crystal device of the present invention works asdiscussed below in a first state of the liquid crystal cell, in whichthe light entering the first absorptive polarizer from the outside istransmitted through the first absorptive polarizer, the liquid crystalcell, and the second absorptive polarizer. Part of the light that isemitted from the second absorptive polarizer and includes a linearlypolarized light component having a polarizing direction parallel to theaxis of reflection of the reflective polarizer is reflected by thereflective polarizer, transmitted through the second absorptivepolarizer and the liquid crystal cell, and emitted from the firstabsorptive polarizer. When the light enters the reflective polarizer onthe opposite side to the second absorptive polarizer in the first stateof the liquid crystal cell, on the other hand, part of the light istransmitted through the reflective polarizer, the second absorptivepolarizer, and the liquid crystal cell in this sequence and emitted fromthe first absorptive polarizer. In this first state of the liquidcrystal cell, the light entering the first absorptive polarizer from theoutside is reflected and emitted to the outside. The light entering thereflective polarizer is also eventually emitted to the outside. Theliquid crystal cell in the first state is accordingly observed as abright pixel both in the reflective display mode and in the transmissivedisplay mode.

[0011] The liquid crystal device works as discussed below in a secondstate of the liquid crystal cell, in which the light entering the firstabsorptive polarizer from the outside is absorbed by the secondabsorptive polarizer. The light supplied from the outside into the firstabsorptive polarizer is absorbed by the second absorptive polarizer, sothat there is no light reflected by the reflective polarizer. Namely thelight entering the first absorptive polarizer from the outside is notemitted from the first absorptive polarizer. When the light enters thereflective polarizer on the opposite side to the second absorptivepolarizer in the second state of the liquid crystal cell, on the otherhand, part of the light is transmitted through the reflective polarizer,the second absorptive polarizer, and the liquid crystal cell in thisorder and enters the first absorptive polarizer. This light is, however,absorbed by the first absorptive polarizer and is thereby not emitted.In this second state of the liquid crystal cell, the light entering thefirst absorptive polarizer from the outside is not emitted to theoutside. The light entering the reflective polarizer is nor emitted tothe outside. The liquid crystal cell in the second state is accordinglyobserved as a dark pixel both in the reflective display mode and in thetransmissive display mode.

[0012] As discussed above, the liquid crystal device of the presentinvention effectively maintains the same bright/dark states in both ofthe reflective and transmissive display modes.

[0013] In accordance with one preferable application, the liquid crystaldevice further includes a diffusing plate interposed between the secondabsorptive polarizer and the reflective polarizer.

[0014] This arrangement effectively suppresses specular reflectionoccurring on the reflective polarizer.

[0015] In accordance with another preferable application of the liquidcrystal device, the predetermined direction of the reflection axis ofthe reflective polarizer is adjusted to cause a ratio of an amount offirst light to an amount of second light to be not less than about 15%in a state where a linearly polarized light component having apredetermined first polarizing direction is emitted in a greatest amountfrom the liquid crystal cell towards the second absorptive polarizer.The first light is one that is reflected by the reflective polarizer andtransmitted through the second absorptive polarizer, the liquid crystalcell, and the first absorptive polarizer. The second light is one thatis incident on the first absorptive polarizer.

[0016] Unlike the conventional liquid crystal display, this arrangementenables non-reversed transmissive display without unduly affecting theadvantageous characteristics (including brightness) of reflectivedisplay.

[0017] In accordance with still another preferable application, theliquid crystal device further includes a backlight disposed opposite tothe second absorptive polarizer across the reflective polarizer. Lightemitted from the backlight is adjusted to have a color other than white,in order to cause color of a first light to be close to color of asecond light. The first light is one that is emitted from the backlightand transmitted through the reflective polarizer, the second absorptivepolarizer, the liquid crystal cell, and the first absorptive polarizer.The second light is one that comes from the outside and is transmittedthrough the first absorptive polarizer, the liquid crystal cell, and thesecond absorptive polarizer, subsequently reflected by the reflectivepolarizer, then transmitted through the second absorptive polarizer, theliquid crystal cell, and the first absorptive polarizer

[0018] In this structure, it is preferable that the backlight includes alight source and a color filter that adjusts color of light emitted fromthe light source.

[0019] This arrangement enables the color of a transmitted lightcomponent that is included in the light emitted from the backlight,transmitted through the reflective polarizer, and emitted from the firstabsorptive polarizer to be adjusted close to the color of a reflectedlight component that is supplied from the outside to the firstabsorptive polarizer, reflected by the reflective polarizer, and emittedfrom the first absorptive polarizer. This reduces a difference in colortone of the display between the reflective display mode and thetransmissive display mode.

[0020] Any one of the above liquid crystal devices may be mounted as adisplay device on a variety of electronic apparatuses.

[0021] These and other objects, features, aspects, and advantages of thepresent invention will become more apparent from the following detaileddescription of the preferred embodiments with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 schematically illustrates the structure of a transflectiveliquid crystal device 100 in a first embodiment according to the presentinvention;

[0023]FIG. 2 illustrates the structure of a reflective polarizer 160;

[0024]FIG. 3 shows the relationship between an axis of transmission 120Tof a first absorptive polarizer 120, an axis of transmission 140T of asecond absorptive polarizer 140, and an axis of reflection 160R of thereflective polarizer 160;

[0025]FIGS. 4A and 4B show functions of the liquid crystal device 100 inthe first embodiment;

[0026]FIG. 5 is a graph showing a variation in reflectivity in areflective display mode and a variation in transmittance in atransmissive display mode in the liquid crystal device 100 of the firstembodiment;

[0027]FIG. 6 schematically illustrates the structure of another liquidcrystal device 200 in a second embodiment according to the presentinvention;

[0028]FIG. 7 shows the relationship between the axis of transmission120T of the first absorptive polarizer 120, the axis of transmission140T of the second absorptive polarizer 140, an optical axis 2100A of aλ/2 phase plate 210, and the axis of reflection 160R of the reflectivepolarizer 160;

[0029]FIG. 8 schematically illustrates the structure of still anotherliquid crystal device 300 in a third embodiment according to the presentinvention;

[0030]FIG. 9 is a graph showing xy chromaticity coordinates of thereflected light and transmitted light that are observed in the firstembodiment shown in the graph of FIG. 5, in an XYZ color specificationsystem;

[0031]FIGS. 10A through 10C show examples of electronic apparatus towhich the liquid crystal device of the present invention is applied;

[0032]FIG. 11 schematically illustrates the structure of a conventionaltransflective liquid crystal device; and

[0033]FIG. 12 shows problems arising in the conventional transflectiveliquid crystal device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A. First Embodiment

[0034]FIG. 1 schematically illustrates the structure of a transflectiveliquid crystal device 100 in a first embodiment according to the presentinvention. The liquid crystal device 100 includes a first absorptivepolarizer 120, a liquid crystal cell 130, a second absorptive polarizer140, a light scattering plate (diffusing plate) 150, and a reflectivepolarizer 160. A backlight 170 is further disposed outside thereflective polarizer 160. Although there is shown a gap between eachelement in FIG. 1, the gap is only for the clarity of illustration. Inan actual device, the respective elements are in close contact with oneanother without any gaps. This is also adopted in other embodiments andmodifications discussed later.

[0035] The liquid crystal cell 130 includes a lower glass substrate 133,an upper glass substrate 131, and a liquid crystal layer 135 sealedbetween these glass substrates 131 and 133. A plurality of transparentsignal electrodes 134 are mounted on the upper surface of the lowerglass substrate 133. A plurality of transparent scanning electrodes 132that are arranged perpendicularly to the signal electrodes 134 aremounted on the lower surface of the upper glass substrate 131. Theliquid crystal layer 135 is composed of a TN (twisted nematic) liquidcrystal composition or STN (super twisted nematic) liquid crystalcomposition. The liquid crystal cell 130 has a simple matrixconfiguration, in which one pixel is defined by one signal electrode134, one scanning electrode 132, and the liquid crystal layer 135between these electrodes 134 and 132. Although there is shown arelatively wide gap between the upper glass substrate 131 and the lowerglass substrate 133 in FIG. 1, this is only for the clarity ofillustration. In an actual device, the upper glass substrate 131 facethe lower glass substrate 133 across a narrow gap of several to ten-oddmicrometers. The liquid crystal cell 130 has color filters, an alignmentlayer, a driving circuit, and other related elements, in addition to theelements illustrated in FIG. 1. For example, color filters areinterposed between the lower glass substrate 133 and the signalelectrodes 134 to be arranged perpendicularly to the scanning electrodes132. The color filters of the respective colors, red (R), green (G), andblue (B) are arranged repeatedly in this sequence corresponding to therespective signal electrodes 134, that is, arranged in stripe. The colorfilters may alternatively be mounted on the upper glass substrate 131.The arrangement of the color filters is not limited to the stripeconfiguration but may have a mosaic configuration. These elements arenot essential for the explanation of the present invention and are thusomitted from the illustration.

[0036] The first absorptive polarizer 120 and the second absorptivepolarizer 140 respectively have the function of transmitting apredetermined linear polarized light component while absorbing the otherlinear polarized light components. The polarizers used in theconventional transmission liquid crystal devices and reflection liquidcrystal devices can be applied for these absorptive polarizers 120 and140.

[0037] The reflective polarizer 160 has the function of reflecting apredetermined linear polarized light component while transmitting theother linear polarized light components. The reflective polarizer 160 ismade of, for example, a birefringent dielectric multi-layered film. Thedetails of the birefringent dielectric multi-layered film are disclosedin International Publication No. WO97/01788 and InternationalApplication-based Japanese Patent Laid-Open Gazette No. 9-506985, thedisclosures of which are herein incorporated by reference for allpurposes.

[0038]FIG. 2 illustrates the structure of the reflective polarizer 160.The reflective polarizer 160 is basically a birefringent dielectricmulti-layered film prepared by alternately placing two different typesof polymer layers 161 and 162 one upon another. One of the two differentpolymers is selected among the materials having a high modulus ofphotoelasticity, whereas the other polymer is selected among thematerials having a low modulus of photoelasticity. It is here noted thatthe selected materials should have substantially equal ordinary indexesin the orientated state. For example, PEN (2,6-polyethylene naphthalate)is selected for the material having the high modulus of photoelasticity,and coPEN (70-naphthalate/30-terephthalate copolyester) is selected forthe material having the low modulus of photoelasticity. Films of thesetwo different polymers were alternately laid one upon another to form afilm laminate, and the film laminate was stretched to approximately 5times in the direction of the x axis in the rectangular coordinatesystem shown in FIG. 2. The observed index of refraction in the x-axisdirection was 1.88 in the PEN layer and 1.64 in the coPEN layer. Theobserved index of refraction in the y-axis direction was about 1.64 inboth the PEN layer and the coPEN layer. When light enters the filmlaminate from the direction of its normal, a light component vibratingin the y-axis direction is transmitted through the film. This is an axisof transmission. A light component vibrating in the x-axis direction is,on the other hand, reflected only when the PEN layer and the coPEN layersatisfy a predetermined condition. This is an axis of reflection. Thepredetermined condition is that the sum of an optical path (that is, theproduct of the index of refraction and the thickness of the film) of thePEN layer and an optical path of the coPEN layer is equal to half thewavelength of light. Lamination of several tens layers or preferablymore than 100 layers of both the PEN layer and the coPEN layer to thethickness of about 30 μm enables reflection of substantially all thelight component vibrating in the direction of the axis of reflection.Changing the number of layers varies the resulting reflectivity. Thereflective polarizer thus manufactured has the polarization ability onlyfor the light of a single design wavelength. In order to attain thepolarization ability in a wider range of the wavelength, a plurality ofreflective polarizers having different design wavelengths are laid oneupon another while their axes of reflection are aligned.

[0039] The sufficiently thick laminate of the reflective polarizer isbrighter by at least 30% than a known reflection polarizer that isprepared by combining a conventional polarizer (absorptive polarizer)with an aluminum reflector. There are two reasons. One reason is thatthe reflective polarizer is a dielectric mirror and thereby reflectsalmost 100% of a specific linearly polarized light component, althoughthe metal aluminum has the reflectivity of not greater than 90%. Theother reason is that the conventional absorptive polarizer takesadvantage of a dichroic dyestuff, such as a halogen like iodine or a dyeand wastes at least 10% of the light because of its relatively lowdichromatic ratio.

[0040] Another liquid crystal polymer having a cholesteric phase may becombined with a λ/4 phase plate and used for the reflective polarizer.The details of such a reflective polarizer are disclosed, for example,Japanese Patent Laid-Open Gazette No. 8-271892, the disclosure of whichis herein incorporated by reference for all purposes.

[0041] The reflective polarizer 160 used in the embodiment does notattain a 100% degree of polarization, so that the reflectivity of thelinearly polarized light component having the polarizing direction thatis parallel to the axis of reflection is several tens percents, whilethe transmittance of the linearly polarized light component having thepolarizing direction that is parallel to the axis of transmission isalso several tens percents. The reflective polarizer 160 reflects partof linearly polarized light components having polarizing directionsother than that parallel to the axis of reflection and transmits part oflinearly polarized light components having polarizing directions otherthan that parallel to the axis of transmission. The degree ofpolarization here is defined either by the reflectivity of light in thedirection of the axis of reflection or by the transmittance of light inthe direction of the axis of transmission.

[0042] The diffusing plate 150 (see FIG. 1) has the function ofdiffusing light. The diffusing plate 150 may be omitted from the liquidcrystal device. In this case, the light specularly reflected by thereflection plate 160 is emitted outside as the return light. Thediffusing plate 150 has the function of preventing the specularreflection. A plastic film with beads dispersed therein, for example,may be used for the diffusing plate 150. In one possible modification,the diffusing plate may be replaced by the second absorptive polarizer140 and the reflective polarizer 160 bonded to each other via an opticaladhesive with beads dispersed therein. The diffusing plate 150 may beinterposed between the first absorptive polarizer 120 and the liquidcrystal cell 130, interposed between the liquid crystal cell 130 and thesecond absorptive polarizer 140, or mounted on the upper surface of thefirst absorptive polarizer 120.

[0043] The backlight 170 includes a light source 171 and a light guideplate 172. Light emitted from the light source 171 is guided anddiffused by the light guide plate 172, in order to enable the light toenter all the pixels in the liquid crystal cell 130. The light guideplate 172 may be a diffusing plate or a laminate of light-collectingprisms. The light source 171 may be a cold-cathode tube or a LED(light-emitting diode). An EL (electroluminescence) surface light sourcemay be used for the backlight 170, instead of the combination of thelight source 171 with the light guide plate 172.

[0044]FIG. 3 shows the relationship between an axis of transmission 120Tof a first absorptive polarizer 120, an axis of transmission 140T of asecond absorptive polarizer 140, and an axis of reflection 160R of thereflective polarizer 160. The axis of transmission 120T of the firstabsorptive polarizer 120 is set to be at right angles to the axis oftransmission 140T of the second absorptive polarizer 140. In thisexample, the axis of transmission 120T of the first absorptive polarizer120 is set to be inclined 45 degrees counterclockwise against thehorizontal direction (the direction of the x axis) in the drawing. Theaxis of reflection 160R of the reflective polarizer 160 is set to berotated clockwise by an angle of θax from the axis of transmission 140Tof the second absorptive polarizer 140. The reflective polarizer 160 hasan axis of transmission 160T that is at right angles to the axis ofreflection 160R.

[0045] The axis of transmission 120T of the first absorptive polarizer120 is set in the direction identical with the polarizing direction oflinearly polarized light that is to be rotated in the liquid crystalcell 130. In the linearly polarized light transmitted through the firstabsorptive polarizer 120, a linearly polarized light component passingthrough the cell area in the OFF state has the polarizing directionrotated by 90 degrees, whereas a linearly polarized light componentpassing through the cell area in the ON state has the unchangedpolarizing direction. The axis of transmission 140T of the secondabsorptive polarizer 140 is set in the direction perpendicular to theaxis of transmission 120T of the first absorptive polarizer 120T, inorder to transmit the linearly polarized light component passing throughthe cell area in the OFF state. The axis of reflection 160R of thereflective polarizer 160 is set to partly reflect the linearly polarizedlight component transmitted through the cell area in the OFF state andthe second absorptive polarizer 140.

[0046]FIGS. 4A and 4B show functions of the liquid crystal device 100 inthe first embodiment. FIG. 4A shows bright display (the cell area in theOFF state), and FIG. 4B shows dark display (the cell area in the ONstate). The description first regards the case in which the backlight170 does not emit light, that is, the reflective display mode. The firstabsorptive polarizer 120 transmits only linearly polarized lightcomponents having the polarizing direction that is parallel to the axisof transmission 120T, among non-polarized rays of light 181 and 182entering the first absorptive polarizer 120, and causes the transmitted,linearly polarized light components to enter the liquid crystal cell130.

[0047] Referring to FIG. 4A, linearly polarized light 181 a, which isemitted from the first absorptive polarizer 120 and enters the cell areain the OFF state, is subjected to rotation of the polarizing directionby 90 degrees in the liquid crystal cell 130 and enters the secondabsorptive polarizer 140 as linearly polarized light 181 b. Since thepolarizing direction of the linearly polarized light 181 b is parallelto the direction of the axis of transmission 140T of the secondabsorptive polarizer 140, the linearly polarized light 181 b is mostlytransmitted through the second absorptive polarizer 140 and enters thereflective polarizer 160 as linearly polarized light 181 c. The linearlypolarized light 181 c entering the reflective polarizer 160 can bedivided into two polarized light components whose polarizationdirections are parallel to the axis of reflection 160R and the axis oftransmission 160T of the reflective polarizer 160, respectively. Thelinearly polarized light component having the poraization directionparallel to the axis of reflection 160R is reflected by the reflectivepolarizer 160 and re-enters the second absorptive polarizer 140 asreturn light 181 d. The return light 181 d re-entering the secondabsorptive polarizer 140 can be divided into two polarized lightcomponents whose polarization directions are parallel to the axis oftransmission 140T and an axis of absorption 140A of the secondabsorptive polarizer 140, respectively. The polarized light componenthaving the porarization direction parallel to the axis of absorption140A is mostly absorbed, while only the polarized light component havingthe porarization direction parallel to the axis of transmission 140Tre-enters the liquid crystal cell 130 as linearly polarized light 181 e.The linearly polarized light 181 e re-entering the liquid crystal cell130 is subjected to rotation of the polarizing direction by 90 degreesin the liquid crystal cell 130 and enters the first absorptive polarizer120 as linearly polarized light 181 f. Since the polarizing direction ofthe linearly polarized light 181 f is parallel to the axis oftransmission 120T of the first absorptive polarizer 120, the linearlypolarized light 181 f is mostly transmitted through the first absorptivepolarizer 120 and emitted. The cell area in the OFF state is accordinglydisplayed as a bright pixel in the reflective display mode.

[0048] Referring to FIG. 4B, on the other hand, linearly polarized light182 a, which is transmitted through the first absorptive polarizer 120and enters the liquid crystal cell 130 in the ON state, is transmittedthrough the liquid crystal cell 130 without rotation of the polarizingdirection and enters the second absorptive polarizer 140 as linearlypolarized light 182 b. The linearly polarized light 182 b entering thesecond absorptive polarizer 140 has the polarizing direction that isparallel to the axis of absorption 140A of the second absorptivepolarizer 140 (that is, the direction perpendicular to the axis oftransmission 140T). The linearly polarized light 182 b is thus mostlyabsorbed by the second absorptive polarizer 140 and is not transmittedthrough the first absorptive polarizer 120. The cell area in the ONstate is accordingly displayed as a dark pixel in the reflective displaymode.

[0049] The liquid crystal cell 130 can be set in an intermediate statebetween the ON state and the OFF state. When the liquid crystal cell 130is in the intermediate state, the state of FIG. 4A and the state of FIG.4B are mixed with each other to attain the display of intermediate tone.

[0050] The following description regards the case in which the backlight170 (see FIG. 1) emits light, that is, the transmissive display mode.The reflective polarizer 160 transmits polarized light components havingthe polarizing direction that is parallel to the axis of transmission160T of the reflective polarizer 160, among non-polarized rays 191 and192 emitted from the backlight 170, and causes the transmitted,polarized light components to enter the second absorptive polarizer 140as polarized light components 191 a and 192 a. The reflective polarizer160, however, has a low degree of polarization and thereby causespolarized light components having polarizing directions other than thatparallel to the axis of transmission 160T to be partially transmitted.The polarized light entering the second absorptive polarizer 140 can bedivided into two polarized light components having the porarizationdirections parallel to the axis of transmission 140T and the axis ofabsorption 140A of the second absorptive polarizer 140, respectively.Only the polarized light component having the porarization directionparallel to the axis of transmission 140T enters the liquid crystal cell130.

[0051] Referring to FIG. 4A, linearly polarized light 191 b, which isemitted from the second absorptive polarizer 140 and enters the cellarea in the OFF state, is subjected to rotation of the polarizingdirection by 90 degrees in the liquid crystal cell 130 and enters thefirst absorptive polarizer 120 as linearly polarized light 191 c. Sincethe polarizing direction of the linearly polarized light 191 c isparallel to the axis of transmission 120T of the first absorptivepolarizer 120, the linearly polarized light 191 c is mostly transmittedthrough the first absorptive polarizer 120 and emitted. The cell area inthe OFF state is accordingly displayed as a bright pixel in thetransmissive display mode, in the same manner as in the reflectivedisplay mode.

[0052] Referring to FIG. 4B, on the other hand, linearly polarized light192 b, which is transmitted through the second absorptive polarizer 140and enters the cell area in the ON state, is transmitted through theliquid crystal polarizer 130 without rotation of the polarizingdirection and enters the first absorptive polarizer 120 as linearlypolarized light 192 c. Since the polarizing direction of the linearlypolarized light 192 c is parallel to the axis of absorption 120A of thefirst absorptive polarizer 120, the linearly polarized light 192 c ismostly absorbed by the first absorptive polarizer 120 and is nottransmitted through the first absorptive polarizer 120. The cell area inthe ON state is accordingly displayed as a dark pixel in thetransmissive display mode, in the same manner as in the reflectivedisplay mode. As discussed above, the transflective liquid crystaldevice 100 of the first embodiment has the same bright/dark states inboth of the reflective display mode and the transmissive display mode.

[0053]FIG. 5 is a graph showing a variation in reflectivity in thereflective display mode and a variation in transmittance in thetransmissive display mode in the liquid crystal device 100 of the firstembodiment. The data in the graph of FIG. 5 are plotted, with angle(hereinafter referred to as the combination angle) θax between the axisof transmission 140T of the second absorptive polarizer 140 and the axisof reflection 160R of the reflective polarizer 160 as abscissa andreflectivity, and transmittance as ordinate, under the condition thatall the pixels in the liquid crystal cell 130 are in the OFF state, thatis, displayed in white. The transmittance and reflectivity in the graphof FIG. 5 are results of the measurement using NPF-EG1228DU(manufactured by NITTO DENKO Co., Ltd.) as the first absorptivepolarizer 120 and the second absorptive polarizer 140 and RDF-C(manufactured by 3M Corp.) as the reflective polarizer 160. The RDF-Chas the functions of both the diffusing plate 150 and the reflectivepolarizer 160 shown in FIG. 1. The standard light source C is used forthe measurement of the transmittance and the reflectivity. Thereflectivity here is defined as the ratio of the intensity of reflectedlight under the condition of the display in the brightest reflectivedisplay mode (that is, the reflective display) in the liquid crystaldevice 100 placed at a predetermined position from the standard lightsource C to the intensity of reflected light from a standard white plateplaced at the same position.

[0054] In this liquid crystal device 100, the combination angle θax isset equal to about 20 degrees as shown in FIG. 3. The graph of FIG. 5gives the reflectivity of about 22.4% and the transmittance of about2.1% for this combination angle θax. In the conventional liquid crystaldisplay described as the prior art, the reflectivity can be enhanced toabout 29%. Although the liquid crystal device 100 of the firstembodiment has a little lower reflectivity but attains substantiallyequivalent brightness. The liquid crystal device 100 further has thesignificant advantage, that is, no reversion of the bright/dark statesbetween the reflective display mode and the transmissive display mode.

[0055] A transflector (for example, an Al/Ag deposit film) may be used,in place of the reflective polarizer, to prevent reversion of thebright/dark states between the reflective display mode and thetransmissive display mode. In this case, however, the reflectivity isabout 15% at most. Compared with this liquid crystal device includingthe transflector, the liquid crystal device 100 of the embodimentattains the sufficiently bright reflective display.

[0056] As described above, the liquid crystal device 100 of the firstembodiment ensures the display without reversion of the bright/darkstates between the reflective display mode and the transmissive displaymode, while maintaining the advantageous characteristics (that is, thereflectivity) of the reflective display.

[0057] It is desirable that the reflectivity of the liquid crystaldevice 100 is not less than about 15%. For that purpose, the combinationangle θax should be set in the range of about 0 degree to 35 degrees:the range Rθax shown in FIG. 5. When the combination angle θax is equalto 0 degree, the reflectivity is about 27.5%, which attains theextremely bright reflective display. The combination angle θaxsufficiently close to 0 degree may, however, cause uneven polarizationof the reflective polarizer 160 to be observed in the transmissivedisplay. The combination angle θax is thus preferably in the range ofabout 0 degree to 30 degrees and more preferably in the range of about15 degrees to 25 degrees. The uneven polarization of the reflectivepolarizer 160 can be relieved by placing a polarizer having an axis oftransmission that is parallel to the axis of transmission 160T of thereflective polarizer 160 between the reflective polarizer 160 and thebacklight 170.

[0058] The above description regards the example, in which the axis oftransmission 120T of the first absorptive polarizer 120 is set in thedirection inclined 45 degrees counterclockwise against the x axis, andthe axis of transmission 140T of the second absorptive polarizer 140 isset to be at right angles to the axis of transmission 120T as shown inFIG. 3. The axis of transmission 140T may be set parallel to the axis oftransmission 120T. In this case, the liquid crystal cell 130 isdisplayed as a bright pixel in the ON state and as a dark pixel in theOFF state. The axis of transmission 120T is not restricted to thedirection inclined counterclockwise 45 degrees counterclockwise againstthe x axis, but is set arbitrarily depending upon the structure of theliquid crystal cell 130.

[0059] The above description regards the specific arrangement in whichthe reflective polarizer 160 has the axis of reflection 160R and theaxis of transmission 160T that are arranged perpendicularly to eachother. This arrangement is, however, not essential, and the axis ofreflection 160R and the axis of transmission 160T may be notperpendicular to each other.

[0060] The above description refers to the specific arrangement of theliquid crystal cell in which the polarizing direction of the lightpassing through the cell area in the OFF state is rotated by 90 degrees,while the polarizing direction of the light passing through the cellarea in the ON state is not rotated. This arrangement is, however, notessential. Another available liquid crystal cell changes the polarizingconditions of light in the ON state and in the OFF state, like anSTN-type liquid crystal cell that takes advantage of the birefringence.Any liquid crystal cell can be used as long as the polarizing directionof light passing through the cell area in the ON state is substantiallyperpendicular to the polarizing direction of light passing through thecell area in the OFF state.

B. Second Embodiment

[0061]FIG. 6 schematically illustrates the structure of another liquidcrystal device 200 in a second embodiment according to the presentinvention. The liquid crystal device 200 has a similar structure to thatof the liquid crystal device 100 of the first embodiment, except that aλ/2 phase plate 210 is interposed between the second absorptivepolarizer 140 and the diffusing plate 150 in the liquid crystal device100 of the first embodiment.

[0062]FIG. 7 shows the relationship between the axis of transmission120T of the first absorptive polarizer 120, the axis of transmission140T of the second absorptive polarizer 140, an optical axis 210OA ofthe λ/2 phase plate 210, and the axis of reflection 160R of thereflective polarizer 160. In the liquid crystal device 200 of the secondembodiment, the axis of transmission 120T of the first absorptivepolarizer 120 is set to be inclined 45 degrees counterclockwise againstthe x axis. The axis of transmission 140T of the second absorptivepolarizer 140 is set to be at right angles to the axis of transmission120T of the first absorptive polarizer 120. The optical axis 210OA ofthe λ/2 phase plate 210 is set to be inclined 45 degrees clockwiseagainst the axis of transmission 140T. Linearly polarized light, havingthe polarizing direction parallel to the axis of transmission 140T,entering the λ/2 phase plate 210 is accordingly converted into linearlypolarized light rotated 90 degrees clockwise , that is, linearlypolarized light having an axis of polarization 210T that is parallel tothe axis of transmission 120T of the first absorptive polarizer 120. Theaxis of reflection 160R of the reflective polarizer 160 is set to beinclined about 20 degrees clockwise against the axis of polarization210T.

[0063] Setting the axis of transmission 120T of the first absorptivepolarizer 120, the axis of transmission 140T of the second absorptivepolarizer 140, the optical axis 210OA of the λ/2 phase plate 210, andthe axis of reflection 160R of the reflective polarizer 160 as shown inFIG. 7 enables the liquid crystal device 200 to ensure the displaywithout reversion of the bright/dark states between the reflectivedisplay mode and the transmissive display mode, while maintaining theadvantageous characteristics of the reflective display, like the liquidcrystal device 100 of the first embodiment.

[0064] The above description refers to the specific arrangement in whichthe λ/2 phase plate 210 is interposed between the second absorptivepolarizer 140 and the diffusing plate 150. The λ/2 phase plate 210 may,however, alternatively be interposed between the diffusing plate 150 andthe reflective polarizer 160. This arrangement exerts almost the sameeffects. A λ/2 phase plate may be used in place of the λ/2 phase plate.

C. Third Embodiment

[0065]FIG. 8 schematically illustrates the structure of still anotherliquid crystal device 300 in a third embodiment according to the presentinvention. The liquid crystal device 300 has a similar structure to thatof the liquid crystal device 100 of the first embodiment, except that acolor filter plate 310 is interposed between the reflective polarizer160 and the backlight 170 in the liquid crystal device 100 of the firstembodiment. The modification from the first embodiment is instead toattain the following effect.

[0066]FIG. 9 is a graph showing xy chromaticity coordinates of thereflected light and transmitted light that are observed in the firstembodiment shown in the graph of FIG. 5, in an XYZ color specificationsystem. The graph of FIG. 9 shows variations in chromaticity coordinatesof the transmitted light and the reflected light against the combinationangle θax in the case of bright display. As clearly understood from thegraph, while the color of the reflected light hardly changes, the colorof the transmitted light is different from the color of the reflectedlight and significantly varies with the combination angle θax. In theliquid crystal device 300 of the third embodiment, the color filterplate 310 is placed between the backlight 170 and the reflectivepolarizer 160, in order to make the color of the transmitted light closeto the color of the reflected light. This arrangement effectivelyreduces a difference in color tone of the display between the reflectivedisplay and the transmissive display.

[0067] Although the liquid crystal device 300 includes the color filterplate 310, the emission spectra of the light source 171 included in thebacklight 170 may be adjusted to reduce the color tone difference whileomitting the color filter plate.

D. Examples of Electronic Apparatus

[0068] The liquid crystal device of the present invention is favorablyapplicable for a display device included in a variety of portableequipment that are used in various environments and desired to have alittle power consumption. FIGS. 10A through 10C show examples ofelectronic apparatus to which the liquid crystal device of the presentinvention is applied.

[0069]FIG. 10A shows a cellular phone having a display unit 802 in anupper section on a front face of a main body 801. FIG. 10B shows a watchhaving a display unit 804 on the center of a main body 803. FIG. 10Cshows a portable information apparatus having a display unit 806 in anupper section of a main body 805 and an input unit 807 in a lowersection thereof.

[0070] These information equipment are used in a variety ofenvironments, indoors and outdoors, and are thus desirable to be drivenwith batteries over a long time period. It is accordingly preferablethat the display device used for these display units 802, 804, and 806has a little power consumption. One known example of the display devicehaving a little power consumption is a reflection liquid crystal devicetaking advantage of natural light. The known reflection liquid crystaldevice, however, can not be used practically in dark surroundings. Theliquid crystal device of the present invention can be used in twodifferent modes, that is, the reflective display mode and thetransmissive display mode. The liquid crystal device of the presentinvention ensures the display without reversion of the bright/darkstates between the reflective display mode and the transmissive displaymode, while maintaining the brightness in the reflective display. Theliquid crystal device of the present invention is thus effectivelyapplied for the electronic apparatuses.

[0071] The above embodiments regard the liquid crystal cells of thesimple matrix configuration. The present invention is, however, alsoapplicable to liquid crystal cells of an active matrix configuration.Although not specifically mentioned in the above embodiments, thepresent invention is applicable to liquid crystal cells for both colordisplay and monochromatic display.

[0072] The examples of the electronic apparatus discussed above are notrestrictive but only illustrative. The liquid crystal device of thepresent invention is applicable to a variety of other electronicapparatuses having a display unit.

[0073] It should be clearly understood that the above embodiments areonly illustrative and not restrictive in any sense. The scope and spiritof the present invention are limited only by the terms of the appendedclaims.

What is claimed is:
 1. A liquid crystal device that modulates lightresponsive to given image signals, the liquid crystal device comprising:a first absorptive polarizer, which receives light from outside; aliquid crystal cell, which receives light emitted from the firstabsorptive polarizer; a second absorptive polarizer, which receiveslight emitted from the liquid crystal cell; and a reflective polarizer,which receives light emitted from the second absorptive polarizer,wherein the reflective polarizer has an axis of reflection in apredetermined direction to reflect at least part of light that has beentransmitted through the first absorptive polarizer, the liquid crystalcell, and the second absorptive polarizer to be incident on thereflective polarizer, and the reflective polarizer partially transmitslight including a linearly polarized light component which is includedin light entering the reflective polarizer from an opposite side to thesecond absorptive polarizer and which is to be transmitted through thesecond absorptive polarizer, and wherein the first absorptive polarizerhas an axis of transmission in a specific direction to cause light,which has been reflected by the reflective polarizer and transmittedthrough the second absorptive polarizer, to be transmitted through thefirst absorptive polarizer.
 2. A liquid crystal device in accordancewith claim 1 , further comprising: a diffusing plate interposed betweenthe second absorptive polarizer and the reflective polarizer.
 3. Aliquid crystal device in accordance with claim 1 , wherein thepredetermined direction of the reflection axis of the reflectivepolarizer is adjusted to cause a ratio of an amount of first light to anamount of second light to be not less than about 15% in a state where alinearly polarized light component having a predetermined firstpolarizing direction is emitted in a greatest amount from the liquidcrystal cell towards the second absorptive polarizer, the first lightbeing one that is reflected by the reflective polarizer and transmittedthrough the second absorptive polarizer, the liquid crystal cell, andthe first absorptive polarizer, the second light being one that isincident on the first absorptive polarizer.
 4. A liquid crystal devicein accordance with claim 2 , wherein the predetermined direction of thereflection axis of the reflective polarizer is adjusted to cause a ratioof an amount of first light to an amount of second light to be not lessthan about 15% in a state where a linearly polarized light componenthaving a predetermined first polarizing direction is emitted in agreatest amount from the liquid crystal cell towards the secondabsorptive polarizer, the first light being one that is reflected by thereflective polarizer and transmitted through the second absorptivepolarizer, the liquid crystal cell, and the first absorptive polarizer,the second light being one that is incident on the first absorptivepolarizer.
 5. A liquid crystal device in accordance with claim 1 ,further comprising: a backlight that is disposed opposite to the secondabsorptive polarizer across the reflective polarizer, wherein lightemitted from the backlight is adjusted to have a color other than white,in order to cause color of a first light to be close to color of asecond light, the first light being one that is emitted from thebacklight and transmitted through the reflective polarizer, the secondabsorptive polarizer, the liquid crystal cell, and the first absorptivepolarizer, the second light being one that comes from the outside and istransmitted through the first absorptive polarizer, the liquid crystalcell, and the second absorptive polarizer, subsequently reflected by thereflective polarizer, then transmitted through the second absorptivepolarizer, the liquid crystal cell, and the first absorptive polarizer.6. A liquid crystal device in accordance with claim 5 , wherein thebacklight comprises: a light source; and a color filter that adjustscolor of light emitted from the light source.
 7. An electronic apparatuscomprising: a display device, the display device including: a firstabsorptive polarizer, which receives light from outside; a liquidcrystal cell, which receives light emitted from the first absorptivepolarizer; a second absorptive polarizer, which receives light emittedfrom the liquid crystal cell; and a reflective polarizer, which receiveslight emitted from the second absorptive polarizer, wherein thereflective polarizer has an axis of reflection in a predetermineddirection to reflect at least part of light that has been transmittedthrough the first absorptive polarizer, the liquid crystal cell, and thesecond absorptive polarizer to be incident on the reflective polarizer,and the reflective polarizer partially transmits light including alinearly polarized light component which is included in light enteringthe reflective polarizer from an opposite side to the second absorptivepolarizer and which is to be transmitted through the second absorptivepolarizer, and wherein the first absorptive polarizer has an axis oftransmission in a specific direction to cause light, which has beenreflected by the reflective polarizer and transmitted through the secondabsorptive polarizer, to be transmitted through the first absorptivepolarizer.
 8. An electronic apparatus in accordance with claim 7 , thedisplay device further comprising: a diffusing plate interposed betweenthe second absorptive polarizer and the reflective polarizer.
 9. Anelectronic apparatus in accordance with claim 7 , wherein thepredetermined direction of the reflection axis of the reflectivepolarizer is adjusted to cause a ratio of an amount of first light to anamount of second light to be not less than about 15% in a state where alinearly polarized light component having a predetermined firstpolarizing direction is emitted in a greatest amount from the liquidcrystal cell towards the second absorptive polarizer, the first lightbeing one that is reflected by the reflective polarizer and transmittedthrough the second absorptive polarizer, the liquid crystal cell, andthe first absorptive polarizer, the second light being one that isincident on the first absorptive polarizer.
 10. An electronic apparatusin accordance with claim 8 , wherein the predetermined direction of thereflection axis of the reflective polarizer is adjusted to cause a ratioof an amount of first light to an amount of second light to be not lessthan about 15% in a state where a linearly polarized light componenthaving a predetermined first polarizing direction is emitted in agreatest amount from the liquid crystal cell towards the secondabsorptive polarizer, the first light being one that is reflected by thereflective polarizer and transmitted through the second absorptivepolarizer, the liquid crystal cell, and the first absorptive polarizer,the second light being one that is incident on the first absorptivepolarizer.
 11. A liquid crystal device in accordance with claim 7 , thedisplay device further comprising: a backlight that is disposed oppositeto the second absorptive polarizer across the reflective polarizer,wherein light emitted from the backlight is adjusted to have a colorother than white, in order to cause color of a first light to be closeto color of a second light, the first light being one that is emittedfrom the backlight and transmitted through the reflective polarizer, thesecond absorptive polarizer, the liquid crystal cell, and the firstabsorptive polarizer, the second light being one that comes from theoutside and is transmitted through the first absorptive polarizer, theliquid crystal cell, and the second absorptive polarizer, subsequentlyreflected by the reflective polarizer, then transmitted through thesecond absorptive polarizer, the liquid crystal cell, and the firstabsorptive polarizer.
 12. An electronic apparatus in accordance withclaim 11 , wherein the backlight comprises: a light source; and a colorfilter that adjusts color of light emitted from the light source.